1. Field of the Invention
The present invention relates to a thermal printhead for performing printing by selectively heating up a plurality of heating dots. The invention also relates to a clip pin used for a thermal printhead.
2. Description of the Related Art
As is known in the art, thermal printhead are designed to selectively supply heat energy to thermosensitive paper or transfer ink ribbon for performing printing. FIG. 13 of the accompanying drawings shows the principal components of a conventional thermal printhead. As illustrated, this conventional printhead includes an insulating primary substrate 1xe2x80x2, a secondary substrate 2xe2x80x2, and a plurality of clip pins 3xe2x80x2 for establishing electrical connection between the primary and the secondary substrates.
The primary substrate 1xe2x80x2 supports drive ICs 6xe2x80x2 covered by a protection coat 7xe2x80x2. The drive ICs 6xe2x80x2 control the operation of a heating resistor 5xe2x80x2 formed on the upper surface of the substrate 1xe2x80x2. The heating resistor 5xe2x80x2 is divided into a multiplicity of small portions or xe2x80x9cheating dotsxe2x80x9d which are selectively heated up by the drive ICs 6xe2x80x2 in accordance with given print data.
In the conventional printhead, a plurality of terminals 8xe2x80x2, connected to e.g. the drive ICs 6xe2x80x2, are provided along the right edge of the substrate 1xe2x80x2. Each of the terminals 8xe2x80x2 is held in contact with the clip portion 3bxe2x80x2 of a relevant one of the clip pins 3xe2x80x2. The lead portion 3axe2x80x2 of each clip pin 3xe2x80x2 extends horizontally from the clip portion 3bxe2x80x2 to be connected to one of the terminal pads 9xe2x80x2 formed on the upper surface of the secondary substrate 2xe2x80x2. The terminal pads 9xe2x80x2 are connected via a wiring pattern (not shown) to a connector 10xe2x80x2 attached to the lower surface of the secondary substrate 2xe2x80x2. In operation, a data transmission cable (not shown), which may be connected to a host computer, is plugged into the connector 10xe2x80x2 for supplying the drive ICs 6xe2x80x2 with signals, data etc. required for performing printing.
The conventional printhead has been found disadvantageous in the following points.
Referring to FIG. 14 of the accompanying drawings, the lead portion 3axe2x80x2 of each clip pin 3xe2x80x2 has a uniform thickness over the entire length thereof. Thus, each clip pin 3xe2x80x2 is rendered rather rigid, so that it will not be bent even when an external force is exerted on the lead portion 3axe2x80x2 (see the arrows A in FIG. 13). The exertion of such external force may occur when the user of the printhead tries to plug a flexible cable into the connector 10xe2x80x2.
Upon application of such external force on the lead portion 3axe2x80x2, the clip portion 3bxe2x80x2 of the clip pin 3xe2x80x2 may be unduly dislocated on the terminal 8xe2x80x2, thereby causing the so-called called xe2x80x9cloose contactxe2x80x9d in relation to the terminal 8xe2x80x2. In an extreme case, the clip portion 3bxe2x80x2 may even be wrenched off the edge of the primary substrate 1xe2x80x2.
The present invention has been proposed under the circumstances described above, and an object of the present invention is to provide a clip pin capable of overcoming the above problems. Another object of the present invention is to provide a thermal printhead using such clip pins.
According to a first aspect of the present invention, there is provided a thermal printhead which includes: a first substrate provided with a heating resistor; a second substrate spaced from the first substrate; and a plurality of connectors bridging between the first and the second substrates. Each connector is formed with an elongated lead portion which is provided with a bend-facilitating part and a relatively rigid part.
According to a preferred embodiment of the present invention, the bend-facilitating part is smaller in thickness than the rigid part.
Preferably, the bend-facilitating part may be greater in width than the rigid part. Further, the bend-facilitating part may be generally equal in cross-sectional area to the rigid part.
The bend-facilitating parts of the respective connectors may be arranged in a single line. More preferably, the bend-facilitating parts may be arranged in at least two lines. In either case, all of the bend-facilitating parts may be disposed between the first and the second substrates.
Preferably, each connector may be provided with a clip portion formed integral with the lead portion.
According to a second aspect of the present invention, there is provided a clip pin for connecting separate electrical units. The clip pin includes: a generally straight lead portion; and a clip portion formed at an end of the lead portion. The lead portion is provided with a bend-facilitating part which is smaller in thickness than a remaining part of the lead portion.
Preferably, the clip portion may include an upper holding part and a lower holding part spaced vertically from the upper holding part. Further, the bend-facilitating part may have a principal surface whose normal extends generally vertically.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.